One currently accepted technique for assessing the severity of a stenosis in a blood vessel is coronary flow reserve (CFR). CFR is a measure for determining whether a stenosis is functionally significant. CFR can be calculated as a ratio of the hyperemic average peak velocity of blood flow to the baseline (resting) average peak velocity. Instantaneous peak velocity (IPV) is the peak observed velocity for an instantaneous Doppler spectrum provided by a Doppler transducer. An exemplary method of calculating an average peak velocity (APV) comprises averaging a set of IPV's over a cardiac cycle. A normal CFR is greater than about 2 and indicates that a lesion is not significant. Lower values may require intervention. CFR may be measured prior to treatment to determine if treatment is required and may be used post-treatment to determine the efficacy of treatment.
Another currently accepted technique for assessing the severity of a stenosis in a blood vessel is fractional flow reserve (FFR). FFR is a calculation of the ratio of a distal pressure measurement (taken on the distal side of the stenosis) relative to a proximal pressure measurement (taken on the proximal side of the stenosis). FFR provides an index of stenosis severity that allows determination as to whether the blockage limits blood flow within the vessel to an extent that treatment is required. The normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and require treatment. Common treatment options include angioplasty and stenting. Some intravascular devices incorporate a combination of sensing elements suitable for measuring both pressure and flow within a vessel, such that FFR and CFR measurements can be made.
Accordingly, there remains a need for improved devices, systems, and methods for assessing the severity of a blockage in a vessel and, in particular, a stenosis in a blood vessel. In that regard, there remains a need for improved devices, systems, and methods for assessing the severity of a stenosis in the coronary arteries with flow-sensing elements.